lL-6 levels are elevated in patients across multiple tumor types, including breast cancer [170,171,172,173,174,175,176,177,178,179,180], and mechanistically, IL-6 has been shown to promote breast cancer stem cell renewal through Notch3 signaling [138] and distant metastasis of breast cancer cells to the lung through STAT3 signaling [181] and to the bone through RANKL signaling [100]. Here, STAT3 is linked to breast cancer.